I. Field of the Invention
This invention relates to a vascular shunt connecting the systemic circulation to the pulmonary circulation as a treatment for children with cyanotic congenital heart diseases, the result of which is decreased pulmonary blood flow. More particularly it relates to a shunt which is most typically used as a palliative procedure to provide increased pulmonary blood flow until the child reaches the body weight deemed necessary for favorable surgical results from a complete "corrective" surgical procedure. As the child grows, increased blood flow through the shunt to the lungs, which have increased in size and mass, is desirable. In order to accommodate increased blood flow, a shunt path or paths are required, the flow area of which can be increased when desired.
II. Historical Background and Description of Related Art Including Information disclosed Under 37 CFR Secs. 1.97 & 1.98
The concept of a vascular shunt connecting the systemic circulation to the pulmonary circulation was first published by Drs. Blalock and Taussig in 1945. This was the first surgical procedure to treat children with cyanotic congenital heart diseases of the type which result in decreased pulmonary blood flow. This procedure continued as the only surgical option for children with cyanotic congenital heart disease until the 1950s when corrective surgical procedures were first attempted. Even though corrective surgical procedures are now regularly undertaken, systemic to pulmonary shunts continue to be a preferred treatment for children with complex cyanotic congenital heart disease. The shunts continue to be used as a palliative procedure which will allow the child to grow, thereby gaining body mass, prior to complete repair of the defective heart by corrective surgical procedures. The growth of the child normally assures better results from the corrective surgical procedures.
The systemic to pulmonary "Blalock-Taussig" or, as they are commonly known, "B-T" shunts, were originally performed by connecting a subclavian artery to a pulmonary artery in a side to end fashion, the so called "classic procedure". The "classic procedure" continued to be used until more than two decades later, when in the 1980s, synthetic material was first used to create a tubular structure for connecting a subclavian artery to a pulmonary artery in a side-by-side fashion. This so-called "modified procedure" is generally regarded as superior to the "classic procedure" since it preserves flow to the upper extremities through the subclavian artery and provides the ability to control the amount of blood flow to the lungs by choosing the size, i.e. the cross-sectional flow area or lumen of the shunt.
A review of developments with respect to the Blalock-Taussig shunt procedure is set forth in: The Blalock-Taussig Shunt: An Analysis of Trends and Techniques in the Fourth Decade, William L. Holman, M.D. et al, Journal of Cardiac Surgery, Vol. 4, No. 2, 1989, pages 113-124.
In many instances the volume of the pulmonary blood flow provided by the "modified procedure" B-T shunt becomes inadequate as the child grows, due to the limited blood volume which will pass through the fixed cross-sectional flow area or lumen of the B-T shunt. When this inadequacy develops, it has been found necessary to implant a second "modified procedure" B-T shunt, typically on the opposite subclavian artery from the first, so as to provide increased pulmonary blood flow until the child reached the body weight deemed desirable for favorable surgical results from a "corrective" surgical procedure.
Clearly, it would be highly desirable to avoid such a second procedure. It being desirable whenever possible to avoid a surgical procedure if the desired benefit to the patient can be provided without again opening the chest cavity. For instance, the necessity for a second through the chest wall invasive procedure could be eliminated if the previously implanted shunt could be dilated, that is increased in cross-sectional area, by a less traumatic procedure, such as by an angioplasty procedure, to accommodate the increased amount of pulmonary blood flow required by a growing child. The desirability of providing such a shunt is the genesis for this invention, which provides an expandable shunt for use in a "modified procedure" B-T shunt.